Irregular
by SackDantOur
Summary: Issei Hyoudou was a normal boy, living a normal life, and then one day a beautiful, not-so-normal, red-haired girl quite literally crashed into his life. Deciding to follow her up the Tower was an impromptu decision, but not necessarily anything new. He'd always been chasing skirts after all; and was pursuing a girl through a multitude of dangerous trials really all that different?


**Full summary:** Issei Hyoudou was a normal, young boy, living a normal life in a normal town, and then one day a Beautiful, not-so-normal, red-haired girl quite literally crashed into his life. Deciding to follow her up the Tower was an impromptu decision, but not necessarily anything new. He'd always been chasing skirts after all; and was pursuing a girl through dangerous trials of – what was at times, actual – fire really all that different?

* * *

**Prologue**

**Posted: 26-10-2019**

* * *

He was old. He was very, very, _very _old. And not very, very, very old by the standards of a mortal, but by the standards of an immortal.

He was not actually a 'he', either. He was an 'it', technically lacking a gender. To his kind – again, technically not a 'he' but an 'it' – reproduction was a non-issue; 'gender' therefore an obsolete concept.

This tended to confuse most mortals though. So in order not to further push the limited thought capacity of the creatures he had interacted with and would likely continue interacting with over the coming millennia, he'd decided to refer to himself using male pronouns.

He'd been waiting for a while now. Something new was about to enter the Tower, and like always, he was to be there and greet it; so he waited. He didn't know if he'd been standing there for but a day, or if it had been a decade since he last moved from the spot he was occupying, and he didn't care, because it didn't matter.

This again, would have likely sounded strange to most mortals, as waiting would quite literally eventually kill them, but when you'd existed for as long as the concept of age itself, time carried remarkably little significance.

And then – during a moment in time which, again, didn't matter – the Tower doors opened, unlocking from the outside, and in crawled a tiny organism.

Headon studied it passively. He didn't miss anything. He never did; not any more.

He saw how blood flowed through the creature, distributing oxygen and nutrients to wherever they were needed. Saw how the muscles contracted and extended, keeping the body upright, along with the organs that were necessary for it to at all function, the most important ones protected behind the rib-cage or the skull. Saw how the multipotent cells in the bone marrow slowly produced white blood cells, which in turn fought valiantly against invading bacteria, keeping the body strong and healthy.

None of these things really helped to identify the creature's race and gender though. For that, Headon would need to look a little closer to the surface.

Mhm... compared to other mortals, it was of average size, if maybe a little smaller. And probably male... yes, the construction of the genitals seemed to suggest this was the case. Most likely human going by the position of its – _his – _limbs, head and shoulder-blades.

An Irregular had entered the Tower.

As previously established, Headon was not human, and therefore did not perceive things the way humans did. His emotions weren't necessarily more complex.

Just... different.

Conveying to an intelligent mortal his thoughts and feelings when presented with the human Irregular would most likely be difficult. Not only because very few languages had evolved far enough to properly describe such complex emotions, but also because the thought process of a Guardian compared to a mortal was just too distinct; one having trouble understanding the other as a result.

If one were to prescribe human emotions to the Guardian, however – his feelings as he silently studied the Irregular – the closest you would come would be 'uncertainty', leading to irritation and maybe... maybe a little fear.

Irregular. It was a word created by mortals, yet describing remarkably well just what they were; what they represented.

If Regulars were the ones _chosen _to climb the Tower, than Irregulars were the ones who _choose _to climb it.

Regulars were an expected existence. Irregulars were not, but still, stubbornly, they did, subsisting in a world they did not belong.

Or maybe they did belong? Only outside expectation and normality.

The tiny amount of uncertainty and irritation bubbling beneath the surface were not born out of any fear of the Irregular's strength. No. If anything, this Irregular was perhaps the weakest Headon had ever encountered, and even the stronger ones had been far from powerful enough to actually pose a threat.

No. The negative feelings directed towards the Irregular existed for a different reason.

Everything inside the Tower was connected. The strings of fate – also called paths – ran from the very top, to the bottom, and then up again, crisscrossing throughout every nook and cranny of the Tower.

Some of the older entities inside the Tower were, in turn, capable of reading these paths, predicting how things would begin, and how they would end.

Headon, being so very, very, _very _old was particularly skilled at this. He knew exactly when a country would rise, and when it would fall. He knew how many baby birds would be born the next thousand years, and when that uniquely small fly currently struggling against a heavy rainfall would plummet to the ground and eventually drown.

He could tell all these things about the future, yet, as he was studying the human in front of him... there was nothing.

Nothing.

His future empty.

That was the thing about Irregulars. Everything born or created inside the Tower were a part of it, bound and limited by its laws. Irregulars on the other hand, having been born on the outside, were not bound by any such laws.

Their path could not be read. Not because they didn't possess one – all living beings did, no matter how small of insignificant – but because it was cut off from the rest of the Tower.

Isolated, yes, but at the same time completely free. And more often than not; unstoppable.

Either way, Headon didn't know if it would be for better or for worse, but things were going to change, as a – would be – powerful new competitor had entered the game.

After all. The Tower only opened its doors to outsiders when it wanted change.

* * *

Holy hell, it actually worked! I'd just sort of charged those floating doors, aiming for a shoulder-tackle and hoping for the best.

I hadn't expected much. Not really.

Contrary to my expectations, however, the doors had given way the moment I'd made contact with them, swinging open as I tumbled inside.

Obviously I'd landed on my face, as gracefully as always, which, to be clear, wasn't very graceful.

Standing up was a bit of a hassle, as my head was still swimming after its brief make-out session with the floor, but I managed it, stumbling upright on shaky legs...

And... wow. Just wow. The place was absolutely breathtaking. Thousands upon thousands of shining crystals, stretching as far as the eye could see, illuminating... well, pretty much everything in a clear, blue color; except for the ceiling, which I couldn't even see.

It was pitch black, likely stretching thousands of meters up into the air.

When footsteps greeted my sensitive hearing, I couldn't help but panic slightly. I'd heard this place would be dangerous, so of course I'd brought something along with me I could use to defend myself. I just hoped it would be enough.

Hefting the large baseball-bat I'd received on my eleventh birthday over my shoulder I turned towards the source of the sound, preparing to either pummel it into the ground or, if its size made that unlikely, hightailing it the hell out of here. There was also a chance it might be friendly, of course, but the way my luck had been going lately, I somehow doubted that would be the case.

Huh...?

It was standing on two legs like a human at the very least, which was good. What was less good was that it still didn't look _anything _like a human, nor any other creature I'd ever seen before.

"Put down your weapon, little one. I won't hurt you." I might have jumped slightly when the voice reverberated through the room. It was deep, dark, and had a strange echoing quality to it.

It sounded damn creepy.

"Yeah..." I started, lowering the bat in my hand slightly while at the same time keeping it in a clear defensive position. "Sorry if I don't take your word for it." It had completely white skin, unblemished with almost a metallic sheen to it. Right were its mouth should have logically been were instead a thin line, moving from one side of its head to the other, making it look like it was smiling. In fact, I would have assumed this was the mouth if it weren't for the pair of tiny lights shining from within the wide line, making it clear it was in fact an opening of some kind. Call me crazy, but I had a feeling those tiny lights were its eyes. And then there were the ears of course, standing up atop its head like a rabbit's.

Come to think of it, its entire head kind of resembled that of a bunny. Although the illusion was shattered as soon as you saw the rest of its body, which was mostly human, or... well, human-like.

"It has been a while since this place had a visitor like yourself." The thing spoke, before lowering itself into an exaggerated bowing motion. "I am known as Headon, the Guardian of this floor." Its head moved up and for a moment I could have sworn the tiny lights within the fissures on its face increased in intensity. "Little one. I welcome you to the Tower."

"So this really is the Tower? I felt a little uncertain, as this place doesn't look anything like what Rias described... Oh, and I'm Issei by the way." I bowed slightly, before righting my posture. It had been friendly enough to introduce itself, so why shouldn't I? No need to be rude.

Come to think of it. Maybe I should stop referring to it as if it were a creature of some kind. I'd never encountered any other intelligent species other than my own, but I knew they existed. After all, Headon was unmistakably a masculine name, and the voice clearly male.

I still didn't trust this completely unknown – clearly not human – stranger. I'd be a fool to. But so far he'd done nothing to suggest he was a threat, and really, I'd like to keep it that way.

So I stayed polite. "Mr... Headon? Should I call you tha-"

"Headon is enough."

"Uh... Okay. Headon. I'm looking for a girl. Rias. She left... a while ago. She promised she'd come back to visit." I huffed, crossing my arms. "And I've been waiting, like I said I would, like I promised..." and I had been waiting, for almost three years now. That was like, forever. "But you know what. I'm tired of waiting. So... uh, I guess I sort of decided to follow her, only, I didn't really know where she went... or how to get there. I knew she was inside something called the Tower... though she said we were already inside it, only the outside part... which would suggest we were not actually inside it... it was confusing."

Headon was just staring at me. Damnit. I'd gone on one of my tangents again, hadn't I? Needed to stop doing that.

"So, anyway. Rias. I think her last name was Zahard or something. Long, flowing, Crimson hair. The figure of a goddess. Have you seen her?"

Headon – he'd called himself a Guardian, which honestly sounded pretty damn cool – placed one hand beneath his chin as if mulling something over, before speaking. "Crimson hair? Oh!"

My smile could have split my face. "So you _have _seen her!? Where? Which way did she go?"

Suddenly the Guardian straightened, and quite literally out of nowhere a staff of some kind materialized. I mean, Rias had shown me some pretty crazy things, but not even she had been able to create things out of thin air. He raised it, pointing upwards. "All you seek lie at the top. Everything you desire. That's all I can tell you."

Ugh! Stupid, cool-sounding, Guardian. Why would you get my hopes up like that? Wait... "Did you just say I can acquire anything I want at the top. _Anything?_" Rias had said something similar, come to think of it, though I hadn't really taken her seriously. Not after she'd laughed in my face once I'd told her my dream. Called it cute, if I remember correctly.

Mrgh... Of course I'd blushed when she'd called it – and by extension me – that. Which only made her laugh harder.

Stupid girls...

"Yes, little one." Headon nodded. "If you want to find your answer, and your girl. Head up. Whether its riches you seek, immortality, magical powers or mysteries, just head up. All the truth, glory and happiness of the world is up there." The lights within the smile-shaped slit on his head suddenly dimmed, before vanishing completely. In their place what could only be teeth appeared, and suddenly eyes had been replaced by a wide, smiling mouth.

That wasn't creepy at all...

It was a smile filled with teeth, and therefore didn't look particularly friendly. Honestly, maybe it was wrong to call it a smile. I mean, it _looked _like one, but it might just as well have been an oddly curled snarl. Well... he didn't sound angry, so probably not, but my point was that his expressions were only remotely similar to the ones I knew... which made sense seeing as we were clearly completely different species.

Headon continued. "So tell me, little one. What do you seek?"

"Okay, first of all. Stop calling me little! Because I'm not. I'm already twelve. And second, I suppose I _could _tell you my dream, but I'm not sure you'd understand." I crossed my arms, huffing as I added quietly to myself. "Rias certainly didn't..."

Headon, however, only shook his head. "I have existed for longer than your entire family line. At this point there is very little I do not know, and even less I would not understand... so go on. What do you seek?"

I huffed to myself. "Why do you want to know so badly?"

He gestured all around him. "This first floor was designed to test Irregulars such as yourself." I was an Irregular? Didn't know what it meant but it sounded pretty cool. "Before I can give you an appropriate test however, I need to first know what it is you seek, for the test is supposed to be proportional to the value of one's wish."

I couldn't help the red rising in my cheeks. "Well, alright then." Seriously, if this guy laughed in my face, the way Rias had, I'd smack him. "I-I'm gonna become a harem king!"

Silence. Just... silence.

And not only because the Guardian didn't say a word, but also because all other sound seemed to just vanish. I couldn't even hear my own breath, and really only knew I was breathing because I _wasn't _currently choking. Even stranger, the quiet appeared to be radiating of off Headon himself, almost as if it was an actual emotion.

No wait. That didn't make any sense. Emotions didn't radiate of off people. That wasn't how they worked...

Still; that was the impression I got. It was a surreal experience. Not necessarily bad, just... weird.

And then the moment was over, and the sound returned, making me wonder if I'd imagined the whole thing.

"You... want to become a king?" The Guardian spoke slowly.

I furrowed my eyebrows in slight irritation. "Wha-what? No. A _harem _king."

"You... you want to rule over a country of women?" He just sounded plain confused at this point.

"Uh... no. That's not it at all! What's the point of ruling over anyone? That's just dumb."

"Then. I'm not sure I understand..."

I sighed, shaking my head. "You claim to know almost everything, and you don't even know what a harem king is? That's like... one of the first things everyone should learn!"

Admittedly, I'd only learned about it by chance myself, when some weird, old guy came by the local playground and told all the kids about the wonders of women and harems. Most of the kids didn't seem all that interested while I'd stayed and listened intently from start to finish about his wild adventurers.

Of course, some of the things he mentioned had gone over my head.

He'd spoken of sex-sfings and something called orgies for example, which I didn't completely get, but women were soft and cuddly, so surely being surrounded by a bunch of them couldn't be a bad thing, right?

I did understand the core of the message though.

I spoke my chain of thoughts out-loud.

"The harem is every man's dream. What every man should strive to acquire. It is an ideal, only the greatest of men can make into reality." I continued proudly. "But I'm not just gonna settle for a simple harem! I'm gonna become a harem king!"

The Guardian stared me down, face unreadable. "And... what exactly is that?" I couldn't help but note he sounded kind of... tired? As if this conversation was literally draining him of energy.

Nonetheless I did my best to explain. "Well... as I mentioned before... the harem king is more of an ideal than anything else, and is therefore hard to describe using words. Still; I'll do my best to explain it to you..."

* * *

35 minutes.

That was how long the boy had spoken for.

And that was also how long Headon had listened.

Of course, since he didn't consider time of any importance, he also didn't actually know how many minutes had ticked by. All he knew was that some random human had been lecturing him on an unreasonable topic, for an unreasonable amount of time.

He felt the topic logically shouldn't have been as complicated as the boy was making it out to be, but because he couldn't read the boy's paths, he couldn't actually tell if the child was right or wrong or if he was speaking the truth, which were all kinds of unnerving and all around upsetting.

"So yeah... that's what makes a harem king. Do you get it?"

Did he get it? No. No, not at all. "Yes. I get it."

Hm? Did he just lie? Headon had to rewind the conversation in his head to double check.

Yes he had. He'd told a lie.

Why? He hadn't told a lie in thousands of years. Hadn't felt the need to.

"I'm glad!" Headon knew this was true as he could quite easily sense the positive feelings wafting off the boy. "Everyone should know what a harem king is! That's important stuff!"

Was it? Was it really?

"So... anyway. You mentioned a test before..? One I needed to clear in order to reach the next floor. What's it gonna be?"

* * *

Issei wanted to know what his test would be.

So did Headon.

The ancient Guardian remained quiet for a little while, without really knowing why. He'd instantly gone through every possible answer he could logically give to the question, yet he had trouble deciding which of them he should give.

The boy scratched his head. "Headon? You in there?"

The Guardian shook himself out of his stupor, and then spent less than a fraction of a millisecond marveling over the fact his kind actually could be pushed into a stupor, before answering. "No... I, I will simply send you along to the next floor."

"What?" The boy asked confused. "I thought you said I needed to clear a test first?"

"I'm making an exception for you."

The Guardian reached over with his will, grabbing a hold of Issei, and with little exertion hefted him – body, Shinsoo, and soul – up a floor, reaching through space to do it, seeing as the two floors were located in completely separate planes.

Issei reached the second floor safely, and Headon was left alone with his thoughts... and his emotions.

No mortal should bother trying to understand them... because as established before, the thought process of a mortal and what most would consider a god-like being, was miles apart.

The _reasons _for Headon's actions, on the other hand, were easier to grasp, to the point even most mortals could comprehend them.

So then, _why did _the Guardian decide to send the Irregular along, without first testing him?

Some might have assumed it was because he had seen something in the boy. A hidden strength only the most perceptive of individuals could discern. That the boy was somehow special, and that this hidden strength had warranted being sent to the next floor without a trial.

All of these reasons were possibilities, but far from the truth. No, the truth was much, much simpler:

Headon had simply grown tired of the human's bullshit, and decided he didn't want to deal with him any more.

* * *

**Kind of curious how this story will be received, seeing as its a crossover between two utterly different pieces of fiction. **

**So? Is it worth continuing? My Danmachi fic will take precedence over this but I am considering updating it alongside _At War with Nature_. **

**Anyway, anyone who got here from the Highschool DXD crossover archive and who haven't read Tower of God should definitely do so. It's wonderfully well written, with equally amazing world building, and definitely deserves more love. The art is kind of... abysmal in the beginning I admit, but don't worry, it get's so, _so _much better. **

**Read for free (and also legally) on Webtoon (just search Google for "Webtoon tower of god"). **


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